subject: Keratoconus And Glasses [print this page] If you rely on contact lenses to correct Keratoconus you may well have days that you just can't tolerate the lenses. Some bright spark will always ask why you don;t just wear glasses. Well no you can give them the details of why this doesn't always work
First a quick reminder of what the disease is.
Keratoconus is a disease of the clear front part of the eye called the cornea. The disease causes the cornea to thin and bulge outward resulting in distorted vision.
The majority of people, unless they have the disease, or know someone that has it, will have never heard the work Keratoconus.
I've been a contact lens wearer for many years. For the most part I get good vision correction and workable vision with them.
Now, Like most people with the condition I've had the days when i cant tolerate the lenses. They start to irritate or even become painful. On those days it's always helpful when someone asks why I don't just wear glasses (yes I am being sarcastic).
It;s not completely accurate to say that spectacles are no good for this eye condition. For early stages or very mild conditons they work just fine.
Once the condition get's beyond a certain point their usefulness becomes almost nonexistent..
To understand the limitations of glasses let's first take a quick look at how your eye works.
The retina, which is right at the back of the eye, is a layer of highly specialised cells. These cells convert light into nerve impulses that your brain then interprets as vision.
Your eye is basically a sphere and so the cornea is curved.
For all this to work three things need to happen
The image must be reduced in size to fit onto the retina.
The light that is scattered must be focused, or brought together, at the exact right place on the surface of the retina.
The image must be curved to match the curve of the retina.
Spectacles are used for correction of vision issues like:
Myopia (nearsightedness) which occurs when a distant object looks blurred because the image comes into focus before it reaches the retina.
Hyperopia (farsightedness) which occurs when a close object looks blurred because the image doesn't come into focus before it gets to the retina..
Astigmatism, a distortion that causes the eye to create a second focal point. Keratoconus often results in a very extreme and irregular Astigmatism
Glasses work very well with a normally shaped eye.
The spectacle lenses are shaped to bend the light (refract it) so that the point at which it comes into focus changes. So, it;s all about getting the image to come into focus at exactly the point that the light hits the retina.
It is possible to correct regular astigmatism with glasses
This is because there is a limited amount of distortion and it is still just a matter of shifting the second focal point to the correct position so that it aligns with the first focal point. In the early stages of Keratoconus a regular Astigmatism may form and spectacles can be used to correct this with great success.
As Keratoconus progresses so the Astigmatism gets worse and increasingly irregular. This can mean that there are many different curves in the surface of the cornea, which results in many focal points being created. Once you reach this stage spectacles simply cannot be aligned to deal with the multiple focal points that now exist.
The practical upshot of this is that the light doesn't get focused properly on the back of the eye, which results in the retina getting an image that is blurred, and often consists of many images overlapping (what I refer to as "Ghosting").
That;s the reason why sticking on a pair of spectacles is not an alternative to wearing contact lenses.
